The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention is related to encapsulated toner compositions comprised of a core comprised of a silane modified polymer resin, and a polymeric shell thereover preferably prepared by interfacial polymerization. Another specific embodiment of the present invention relates to encapsulated toner compositions comprised of a core comprised of a silane-modified polymer resin, and dye or pigment particles, which core is encapsulated by a polymeric coating such as a polyurea, polyurethane, polyamide, polyester, or mixtures thereof. In another embodiment of the present invention, there is provided an encapsulated toner composition comprising a core of silane modified polymer resin and a silane modified pigment, and encapsulated thereover a polymeric shell. In a specific embodiment of the present invention, there are provided encapsulated toner compositions comprised of a polymeric shell and a core comprised of dyes, pigments or mixtures thereof, and a copolymer of a monomer or monomers and a silane component which can be optionally partially grafted onto the surface of the pigment particles, thus rendering the pigment particles hydrophobic and compatible with the core polymer resin. Examples of advantages associated with the toner compositions of the present invention include the elimination or the minimization of image ghosting, improved toner fixing characteristics, superior release properties enabling their selection, for example, in imaging systems wherein a release fluid such as a silicone oil is avoided, no or minimal toner agglomeration, excellent powder flow characteristics, no or minimal leaching of the core components, and avoidance of core resin component adherence to, for example, dielectric receivers or photoreceptors. Other toner advantages relate to the surface modification of the pigments such as magnetites with suitable organosilane materials. The surface modification of pigment particles through grafting of core polymer resin with suitable organosilane components renders the pigment materials, such as magnetites, hydrophobic, thus improving their compatibility with the core polymer resin and their dispersibility within the toner core composition. Also, the modification of magnetite surfaces also enhances the magnetite's retentivity for the core polymer resin, and improves its adhesion characteristics to paper. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ionographic processes. Preferably, the toner compositions are selected for pressure fixing processes wherein the image is fixed with pressure. Pressure fixing is common in ionographic processes in which latent images are generated on a dielectric receiver such as silicon carbide, reference copending application U.S. Pat. No. 4,885,220 entitled Amorphous Silicon Carbide Electroreceptors, the disclosure of which is totally incorporated herein by reference. The latent images can then be toned with a conductive toner by inductive single component development, and transferred and fixed simultaneously (transfix) in one single step onto paper with pressure. Specifically, the toner compositions of the present invention can be selected for the commercial Delphax printers such as the Delphax S9000, S6000, S4500, S3000, and Xerox printers such as the 4060.TM. and 4075.TM. wherein, for example, transfixing is utilized. In another embodiment of the present invention, the toner compositions of the present invention can be utilized in xerographic imaging apparatuses wherein image toning and transfer are accomplished electrostatically, and transferred images are fixed in a separate step by means of a pressure roll with or without the assistance of thermal energy fusing.
The toner compositions of the present invention can, in one specific embodiment, be prepared by first dispersing the toner precursor component materials into stabilized microdroplets of controlled droplet size and size distribution, followed by shell formation around the microdroplets via interfacial polymerization, and subsequently generating the core polymer resin by in situ addition polymerization, preferably free-radical polymerization within the newly formed microcapsules. Thus, in one embodiment, the present invention is directed to a process for the simple, and economical preparation of pressure fixable encapsulated toner compositions by interfacial/free-radical polymerization methods wherein there are selected as the core polymer resin precursors an addition-type monomer, or monomers and a polyfunctional organosilicon compound capable of undergoing addition polymerization as well as condensation reactions, a colorant including pigments, dyes or mixtures thereof, and shell-forming monomers capable of undergoing interfacial polymerization. Other process embodiments of the present invention relate to, for example, interfacial/free-radical polymerization processes for obtaining encapsulated colored toner compositions. Further, in another process aspect of the present invention the encapsulated toners can be prepared without organic solvents as the diluting vehicle or as a reaction medium, thus eliminating explosion hazards associated therewith; and furthermore, these processes therefore do not require expensive and hazardous solvent separation and recovery steps. Moreover, with the aforementioned process of the present invention there is obtained improved product yield per unit volume of reactor size since, for example, the extraneous solvent component can be replaced by liquid core and shell monomers. The aforementioned toners prepared in accordance with the process of the present invention are, as indicated herein, useful for permitting the development of images in reprographic imaging systems, inclusive of electrostatic imaging processes wherein pressure fixing, especially pressure fixing in the absence of heat, is selected.
Encapsulated and cold pressure fixable toner compositions are known. Cold pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since the toner compositions used can be fused at room temperature. Nevertheless, many of the prior art cold pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions must usually be fixed under high pressure, which has a tendency to severely disrupt the toner fixing characteristics of the toner selected. This can result in images of low resolution, or no images whatsoever. Also, with some of the prior art cold pressure toner compositions substantial image smearing can result from the high pressures used. The high fixing pressure also generates in some instances glossy images and objectionable paper calendering problem. Additionally, the preparative processes of the prior art pressure fixing toner compositions usually employ organic solvents as the diluting vehicles and reaction media, and these would drastically increase the toner's manufacturing cost because of the expensive solvent separation and recovery procedure, and the necessary precautions that have to be undertaken to prevent the solvent associated hazards. Moreover, the involvement of an organic solvent in the prior art processes also may decrease the product yield per unit volume of reactor size. In addition, the solvents in many prior art processes may have deleterious effects on toner particle morphology and bulk density as a result of their removal from the toner particles during the toner isolation stage, thus causing shrinkage or collapse of the toner particles, resulting in a toner of very low bulk density, which disadvantages are substantially eliminated with the process of the present invention. Furthermore, with many of the prior art processes narrow size dispersity toner particles cannot be easily obtained by conventional bulk homogenization techniques as contrasted with the process of the present invention wherein narrow size dispersity toner particles can be obtained. More specifically, thus with the encapsulated toners of the present invention, control of the toner physical properties of both the core and shell materials can be desirably achieved. Specifically, with the encapsulated toners of the present invention undersirable leaching or loss of core components is avoided, and image ghosting is eliminated, in many instances, primarily in view of the presence of a silane core polymer resin, and/or silane modified pigment particles as illustrated herein. Image ghosting is one of the common phenomena in ionographic printing processes. This refers to the unwarranted repetitious generation of images, and is related to the contamination of dielectric receiver by residual toner materials which cannot be readily removed in the cleaning process. The result is the retention of latent images on the dielectric receiver surface after cleaning, and the subsequent unwarranted development of these images. One of the common causes of image ghosting is related to the leaching of the sticky core polymer resin out to the toner's surface, leading to their adherence to the dielectric receiver during the image development process.
In a patentability search report, there was recited the following prior art, all U.S. Pat. Nos. 4,770,968 directed to polysiloxane butadiene terpolymer toner resins, reference for example column 4, and note the formulas of FIGS. 1 to 6, including FIG. 2B, which toners can be selected wherein silicone release oils are avoided, with no apparent teaching in this patent directed to encapsulated toners; 4,814,253 directed to encapsulated toners comprised of domains containing a polymer component having dispersed therein a release composition and thereover a host resin component comprised of toner resin particles and pigment particles, see for example the Abstract of the Disclosure and column 4, and note column 4 wherein there is illustrated as one of the components of the encapsulated toner domains comprised of styrene butadiene block polymers such as Kraton, styrene copolymers, or styrene siloxanes, which components have entrapped or dissolved therein mineral oils or silicon oils; and as background interest 4,430,408 relating to developer compositions containing a fluorene modified alkyl siloxane and a surface treatment carbon black, reference the Abstract of the Disclosure, for example; 4,758,491 relating to dry toner and developer compositions with a multiphase polyorgano siloxane block or graft condensation copolymer, which provides polyorgano siloxane domains of a particular size and concentration at the toner particle surfaces; and 4,820,604 directed to toner compositions comprised of resin particles, pigment particles, and a sulfur containing organo polysiloxane wax such as those of the formulas illustrated in the Abstract of the Disclosure.
There is disclosed in U.S. Pat. No. 4,307,169 microcapsular electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there is disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization processes are also selected for the preparation of the toners of this patent. Also, there is disclosed in the prior art encapsulated toner compositions containing in most instances costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
Liquid developer compositions are also known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments, and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as poly(vinyl pyrrolidone). Additionally, there is described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically, or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Moreover, illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process.
Disclosed in copending application U.S. Ser. No. 395,689 entitled Encapsulated Toner Compositions, the disclosure of which is totally incorporated herein by reference, are encapsulated compositions containing cores comprised of a fluorocarbon and a monomer or monomers. More specifically, there is illustrated in the aforementioned application an encapsulated toner composition comprised of a core with a fluorocarbon-incorporated resin binder, pigment or dyes, and a polymeric shell; and an encapsulated toner composition comprised of a core comprised of a fluorocarbon-incorporated resin binder derived from the copolymerization of an addition-type monomer and a functionalized fluorocarbon compound represented by Formula (I), wherein A is a structural moiety containing an addition-polymerization functional group; B is a fluorine atom or a structural moiety containing an addition-polymerization functional group; and x is the number of difluoromethylene functions, pigment or dyes, and a polymeric shell. Also, illustrated in U.S. Ser. No. 395,677 entitled Encapsulated Toner Compositions, the disclosure of which is totally incorporated herein by reference, is an encapsulated toner composition comprised of a core comprised of pigments or dyes, and a polysiloxane-incorporated core binder resin, which core is encapsulated in a shell.
Accordingly, there is a need for encapsulated toner compositions with many of the advantages illustrated herein. More specifically, there is a need for encapsulated toners wherein image ghosting is eliminated or minimized. Also, there is a need for pressure fixable encapsulated toners which offer quality images with good fixing levels, for example over 70 percent at low fixing pressure of, for example 2,000 psi. Moreover, there is a need for encapsulated toners, including colored toners wherein image ghosting, and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with excellent release characteristics enabling their selection in imaging systems without the use of surface release fluids such as silicone oils to prevent image offsetting to the fixing or fuser roll. Furthermore, there is a need for encapsulated toners, including colored toners with substantially no toner agglomeration, long shelf life exceeding, for example, one year, and wherein the core polymer resin is a silane modified polymer resin. Also, there is a need for encapsulated toners that have been surface treated with additives such as carbon blacks, graphite or the like to impart to their surface certain conductive characteristics such as providing a volume resistivity of from about 1.times.10.sup.3 ohm-cm to about 1.times.10.sup.8 ohm-cm. Furthermore, there is a need for encapsulated toners wherein surface additives such as metal salts or metal salts of fatty acids and the like are utilized to assist in the release of the images from the imaging component to the paper substrate. There is also a need for simple and economic processes for the preparation of encapsulated toners. Specifically, there is a need for interfacial/free-radical polymerization processes for black and colored encapsulated toner compositions comprised of a hard polymeric shell and a soft core containing a silane-modified polymer resin and silane-modified pigment particles, and wherein organic solvents are eliminated in their preparation in some embodiments. Moreover, there is a need for enhanced flexibility in the design and selection of the shell and core materials for pressure fixable encapsulated toners, and/or flexibility controlling the toner physical properties such as the bulk density, particle size, and size dispersity.